Field of the Invention
The present invention relates to a foam removing device and a foam removing method, which remove foam by a centrifugal separation system, where centrifugal separation is performed on a foam-containing liquid containing air bubbles.
Description of the Related Art
As for a foam removing device for removing foam, conventionally known is a device in which a cylindrical liquid container for accommodating a foam-containing liquid containing air bubbles is rotated with a cylindrical axis thereof as a center, to act centrifugal separation on the foam-containing liquid (see Japanese Patent Application Laid-Open (JP-A) No. 2007-289814). In such a foam removing device, among the air bubbles and the liquid constituting the foam-containing liquid, the air bubbles formed of air having small specific gravity are concentrated in an area adjacent to the cylindrical axis as the liquid container is rotated and the centrifugal separation is acted on the foam-containing liquid. Meanwhile, the foam-removed liquid, from which the previously contained foam has been removed by concentrating the air bubbles in the area adjacent to the rotating axis, has larger specific gravity than air for forming the air bubbles, and therefore the foam-removed liquid moves in the direction far from the rotating axis, i.e., towards the cylindrical internal perimeter surface of the liquid container.
As a result, the cir bubbles concentrated in the center of the cylindrical axis, and the foam-removed liquid moved towards the internal perimeter surface of the liquid container are discharged outside through different outlet pipes, and therefore the foam-removed liquid, from which air bubbles have been removed, can be attained.
In the foam removing device disclosed in JP-A No. 2007-289814, a foam-containing liquid supply pipe, which is configured to supply a foam-containing liquid, is connected to one end of the liquid container relative to the cylindrical axis direction, and a foam-containing liquid supply opening is formed. Moreover, a foam-removed liquid outlet pipe, which is configured to guide the foam-removed liquid to outside of the liquid container, is connected to the other end of the liquid container relative to the cylindrical axis direction, and a foam-removed liquid outlet opening is formed. The foam-containing liquid supply pipe and the foam-removed liquid outlet pipe are liquid transport pipe each in the shape of a circular pipe, and are provided in the manner that a center of a cross-section thereof is aligned on the cylindrical axis of the liquid container.
Moreover, the air bubble outlet pipe for guiding the air bubbles outside the liquid container is provided in the foam-containing liquid supply pipe in the manner that it is go through a center of a cross-section of the foam-containing liquid supply pipe. The air bubble outlet pipe is a circular pipe member having an outer diameter sufficiently smaller than an inner diameter of the foam-containing liquid supply pipe, and has a structure where the foam-containing liquid is passed through the space between the internal perimeter surface of the foam-containing liquid is supply pipe and the outer perimeter surface of the air bubble outlet pipe to be supplied into the liquid container.
The foam-containing liquid supply pipe and the foam-removed liquid outlet pipe are not rotatable, and at the connection thereof with the rotatable liquid container, a pipe coupling having a shaft bearing function, so-called a rotary joint, which can rotatably connect with the liquid container, is provided. Meanwhile, the air bubble outlet pipe is provided inside the foam-containing liquid supply pipe, and has a structure that it extends to the position where the air bubbles are concentrated inside the liquid container. No connection is provided between the air bubble outlet pipe and the liquid container. Moreover, a separation plate, which is configured to prevent air bubbles from entering the foam-removed liquid outlet opening, is provided between the air bubble outlet opening, which is formed in the air bubble outlet pipe in the manner that it receives the air bubbles concentrated in the area adjacent to the cylindrical axis, and the foam-removed liquid outlet opening for sending the liquid in the liquid container into the foam-removed liquid outlet pipe. This separation plate is a disk member diameter of which is smaller than the inner diameter of the cylindrical liquid container. Then, the separation plate is a member for blocking a flow cannel of the air bubbles concentrated in the area adjacent to the cylindrical axis towards the foam-removed liquid outlet opening, and moving the liquid adjacent to the internal perimeter surface to the form-removed liquid outlet opening through a space between the outer perimeter edge thereof, and the internal perimeter surface of the liquid container.
In the foam-separation device disclosed in JP-A No. 2007-289814, the foam-containing liquid supplied into the liquid container through the foam-containing liquid supply pipe is rotated inside the liquid container. As a result of the action of the centrifugal separation due to the rotation, the air bubbles in the foam-containing liquid are concentrated to the area adjacent to the cylindrical axis, enter into the air bubble outlet pipe from the air bubble outlet opening, and then are discharged outside the liquid container.
Meanwhile, a liquid component of the foam-containing liquid moves, as a foam-removed liquid, in the direction far from the cylindrical axis, i.e., towards the internal perimeter surface of the liquid container, as the centrifugal separation acts due to the rotation. Thereafter, the foam-removed liquid is passed through a space between the internal perimeter surface of the liquid container and the separation plate, enters into the foam-removed liquid outlet pipe from the foam-removed liquid outlet opening, and then is discharged outside the liquid container.
In the manner as described, the air bubbles concentrated at a center of the cylindrical axis, and the foam-removed liquid moved towards the internal perimeter surface of the liquid container can be discharged outside the liquid container through different outlet pipes, and the foam-removed liquid, from which air bubbles have been removed, can be attained.
To maintain the performance of the foam removing device, inside of the liquid container is regularly washed. As for the washing, at least either the connection between the foam-containing liquid supply pipe and the liquid container, or the connection between the foam-removed liquid outlet pipe and the liquid container needs to be released. However, the pipe coupling having a shaft bearing function has a complicated structure compared to the pipe coupling having no shaft bearing function, and it takes time for releasing the connection, which increases the operational loads.
When the components are reconnected after releasing the connection, it is necessary to connect in the sealed state so as not to cause leakage of the liquid, and therefore it also takes time for reconnecting, which increases the operational loads.
Further, if the central axis of the connection at the side of the foam-containing liquid supply pipe functioning as the shaft bearing, and that of the connection at the side of the foam-removed liquid outlet pipe are not accurately matched, the rotating axis is sifted during the rotation of the liquid container, and therefore the sealing cannot be maintained, which may cause leakage of a liquid. Accordingly, it is necessary to c connect to accurately match the central axes of the two connections, which leads to a significant increase of the operational loads during the connection.